1. Field of the Invention
The present invention relates generally to dust control systems. More specifically, the invention relates to a dust control system for transferring material from an upper conveyor to a lower conveyor. During transfer of the material, the present invention minimizes induced airflow through the transfer device and across the material. In this manner, dust emanating from the material during transfer of the material is greatly reduced during transfer. Furthermore, the invention allows there to be adjustable capacity of the chute so that flow of material through the chute may be permanently or temporarily increased easily.
2. Description of the Related Art
When material such as coal, minerals or grains are transferred from one place to another, fugitive dust is inherently created by air flowing through the material during the transfer process. As material falls or is projected from a first position to a second position (for instance, from an upper conveyor to a lower conveyor), a stream is formed. The particles in the stream impart frictional drag on the surrounding air. The surrounding air begins to flow downward in the general direction of the material stream. This is called an induced airflow. At the end of the fall or projection, the velocity of the airflow is converted into static pressure due to the sudden stop of the material stream. This static pressure creates an area of high air pressure.
The area of high air pressure must flow into an area of lower air pressure. As this occurs, the small particles of the material are suspended in the air, creating a dust. Such dust emanates from the material (as evidenced by a cloud of dust emanating from the termination of the projection or fall of the material), contaminating the air and leaving a light film on everything in the vicinity of the material transfer device. Such material dust is often harmful to breathe and often the dust is explosive and frequently causes fires or explosions. In fact, fugitive dust emanating from such materials is heavily regulated by the Occupational Safety & Health Administration (OSHA) and in the mining industry, the Mine Safety and Health Administration (MSHA).
Various passive systems have been employed over the years to help reduce such fugitive dust during transfer of material from a first location to a second location. Generally, such passive systems use a housing surrounding the material transfer devices to contain air carrying suspended particles and to prevent the contaminated air from being vented into the ambient environment. The housing creates a region of low pressure therein to draw in the contaminated higher air pressure. Examples of such systems are fully disclosed in U.S. Pat. No. 6,000,553 to Bradbury, et al. and U.S. Pat. No. 6,176,368 to Bradbury, et al.
Active methods and systems of attempting to control such fugitive dust include filtering the dust into a filtration system, or wetting the material with chemicals to weigh down the lighter dust particles. Beyond consolidating the stream of material which is employed in conjunction and at time mutually exclusive from passive control, none of the active or passive systems for controlling fugitive dust take complete measures to reduce the induced airflow from the material as it falls or is projected. Therefore, it is desirable to have a system that substantially reduces fugitive dust by reducing induced airflow through the material as it is transferred from an upper location to a lower location.